RU2515642C2 - Method of obtaining optic ceramics - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of obtaining optic ceramic material includes synthesis of initial raw material powder, thermal processing in mould with obtaining porous briquette, hot monoaxial recrystalisation pressing of powder briquette and thermal processing of obtained ceramics in active fluorinating medium. Synthesis of initial raw material is realised in interaction of mixture of carbonic salts of alkali-earth and rare-earth metals and solution of hydrofluoric acid, which results in obtaining synthesised powder of fluorides of alkali-earth and rare-earth elements, which is briquetted by processing in vacuum at temperature 1000-1350°C and pressure 10^-4-10^-5 mm Hg for 1-3 hours.

EFFECT: obtaining optic ceramics based on fluorides of alkali-earth metals with alloying addition of fluorides of rare-earth metals, which are characterised by high transparency to radiation with wave length 0,2-10 mcm and demonstrating, depending on composition, scintillation or laser properties.

3 cl, 1 tbl, 5 ex, 8 dwg

Description

The invention relates to a technology for producing optical polycrystalline materials, and in particular to a method for producing a wide class of compounds of fluoride ceramics based on fluorides of alkaline earth and rare earth elements having properties of a wide spectrum of action in the form of laser and scintillation materials.

The latest high-tech developments of laser and scintillation materials based on barium and calcium fluorides with dopants of alkaline-earth and rare-earth elements with laser or scintillation properties depending on the selection of a specific material composition are known from the prior art.

In the patent of the Russian Federation No. 2321120, published March 27, 2008 under the IPC index H01S 3/16, the group of inventions "Laser fluoride ceramics and method for its preparation" is protected, where the initial mixture of metal fluorides contains a base in the form of one or more fluorides from the group of alkaline earth metals and a dopant capable of forming a homogeneous solid solution with a fluorite structure with a base at a molar ratio of 50-99 / 50-1, while the initial mixture contains components with an excess of fluorine introduced into them. A method for producing ceramics involves hot pressing an initial mixture of ground fractions of fluorides of alkaline earth and rare earth metals at a temperature of at least 900 ° C using an active fluorinating medium. The technical result consists in creating a highly transparent laser material suitable for transmitting, generating and converting photon radiation with different frequencies and powers of optical signals, including those that are unattainable for single crystals.

In the patent of the Russian Federation No. 2436122, published December 10, 2011 according to the IPC index G01T 1/20, the group of inventions “Method for producing scintillation ceramics and scintillator” is protected. The technical result, which consists in creating a scintillator having ultrashort (subnanosecond) luminescence time and high light output, is achieved by a method for producing scintillation ceramics, including uniaxial hot pressing of high-purity BaF ₂ -ScF ₃ in the form of a monolithic material, which is a solidified melt, or single crystal, or a powder mixture with a dopant concentration of 0.05 to 5.0 mol.%, at a temperature of 1000-1250 ° C and a pressure of 100-200 MPa until ceramic is formed and subsequent annealing of the floor ceramics in a gaseous atmosphere CF4.

In the patent of the Russian Federation No. 2436877, published on December 20, 2011 according to the indices MPK С30В 28/02, С30В 33/02, С30В 29/12, С04В 35/553, С04В 35/622, H01S 3/16 and В82В 3/00, the method is described obtaining fluoride nanoceramics, which includes thermomechanical processing of the initial crystalline material made of metal halides at a plastic deformation temperature, obtaining a microstructured substance characterized by a crystal grain size of 3-100 μm and a nanostructure inside the grains. In this case, the thermomechanical treatment of the starting material is carried out in a vacuum of 10 mmHg, reaching a degree of deformation of the starting crystalline material by 150 to 1000%, resulting in a polycrystalline nanostructured material, which is compacted at a pressure of 1-3 tf / cm ² to achieving theoretical density, and then annealing in the active medium of the fluorinating gas. The method allows to obtain optical ceramics having high laser and lasing characteristics.

As a starting crystalline material, it is possible to use a finely dispersed powder that has undergone heat treatment in gaseous carbon tetrafluoride or without such treatment, if the starting material has a special degree of purity. Another variant of the initial crystalline material may be the use of a molded preform of a given size, obtained from a powder.

The initial billet may be a sintered billet of fine powder that has undergone heat treatment in an atmosphere of carbon tetrafluoride, and the crystalline form of the substance, including a single crystal of a given composition, can also be used.

For the prototype of a new method for producing optical ceramics, RF patent No. 2436877 was selected.

The objective of the present invention is to obtain an optical ceramic based on alkaline earth metal fluorides (Ba or Ca) with a dopant of rare earth metal fluorides (Nd, Yb, Er, Ce, Sc, Tm), characterized by high transparency for radiation with a wavelength of 0.2-10 μm and showing, depending on the composition, scintillation or laser properties.

The technical result is achieved by the universality of the method for producing an optical ceramic material, which includes synthesis of the initial raw material powder for hot pressing, heat treatment of the initial powder to obtain a porous powder briquette, hot uniaxial recrystallization pressing of the powder briquette, and heat treatment of the obtained ceramic in an active fluorinating medium.

The method for producing an optical ceramic material of the present invention includes several steps, namely: synthesis of a raw powder with a given composition; heat treatment of the powder and obtaining briquettes for hot pressing; uniaxial hot recrystallization pressing of powder briquettes; heat treatment of pressed ceramic samples in an active fluorinating gas medium. Unlike the prototype, the raw materials used are powders obtained by the interaction of hydrofluoric acid with carbon salts of alkaline earth and rare earth elements, and the heat treatment of the starting powders takes place in vacuum. The synthesized powder of fluorides of alkaline earth and rare earth elements is briquetted by treatment in vacuum at a temperature of 1000-1350 ° C and a pressure of 10 ^-4 -10 ^-5 mm Hg within 1-3 hours.

The resulting optical ceramic has a transparency region in the wavelength range from 0.2 to 10 μm and, depending on the composition, exhibits laser or scintillation properties.

For the manufacture of optical ceramics, a mixture of alkaline earth and rare earth fluorides of the following composition is used: MeF ₂ -X% TRF ₃ , where Me = Ba, Ca, a TR = Nd, Yb, Er, Ce, Sc, Tm, X is the concentration of the dopant, varying from 0.01 to 10 mol.%.

The initial mixture in the form of carbonic salts of barium fluorides, calcium and rare earth elements is obtained using carbonates of selected specific starting components by their interaction with a concentrated 45-50% solution of hydrofluoric acid, which allows you to get a clean powder, free from reaction by-products.

Powder synthesis.

For the synthesis of powders were used carbonate salts of calcium, barium, rare earth elements and 40-50% solution of hydrofluoric acid. All used chemical reagents were classified by purity - especially pure (TSP) with an impurity content of 10 ^-5 -10 ^-10 %. The synthesis was as follows. Carbonate salts of alkaline earth metal and rare earth metal in the form of powders in a certain ratio were mixed and added to a 40-50% solution of hydrofluoric acid. Moreover, the amount of acid solution was taken with a 5-10% excess in relation to the required amount of acid according to the calculation. As a result, co-precipitation of alkaline earth and rare earth fluoride occurred. The reaction proceeded in an acidic medium at pH = 1-2.5, which contributed to the complete exclusion of the presence of unreacted carbonic salts in the reaction product. Residues of hydrofluoric acid (5-10%) were present in the synthesized mixture of fluorides of alkaline earth and rare earth elements, which subsequently prevented the formation of pyrohydrolysis of the synthesized fluorides and the undesired formation of oxyfluorides and hydroxyfluorides at the drying and calcining stages. The reaction product was dried at a temperature of 90-100 ° C, after which the moisture content in fluoride was at the level of 3%. Complete dehydration of fluorides and the removal of residues of hydrofluoric acid was achieved during calcination at a temperature of 600-800 ° C. The content of the main substance after the calcination step was 99.95 ± 0.05%.

Heat treatment of synthesized powder - briquetting. In order to increase the purity of the synthesized raw powder and to obtain a briquette convenient for hot pressing, it was processed at a high temperature, which was carried out as follows. The synthesized powder was placed in a mold with a lid made of a heat-resistant alloy. The dimensions of the mold were determined by the dimensions of the future ceramic blank. The powder form was installed in a vacuum oven, in which a pressure of 10 ^-4 -10 ^-5 mm Hg was created. and supported by the vacuum system of the furnace during the entire process of heat treatment of the powder. Next, the furnace was heated to a temperature of 1000-1350 ° C, did isothermal exposure for 1-3 hours, after which the heating of the furnace was turned off, and the latter inertially cooled to 30 ° C. Vacuum heat-treated powder had the form of a porous briquette suitable for hot pressing.

Hot uniaxial recrystallization powder briquette pressing.

The powder briquette was subjected to hot pressing, which was carried out in a vacuum oven combined with a hydraulic press. The powder briquette was placed in a mold made of heat-resistant alloy. The briquette mold was placed in a vacuum oven. The furnace was installed with its base on a steel plate of a hydraulic press, and from above it rested against a steel plate of a beam. In the working chamber of the furnace, a system of vacuum pumps created a pressure of 10 ^-3 -10 ^-4 mm Hg. and maintained throughout the process. The furnace was heated to a temperature of 900-1200 ° C in 1-2 hours. Then did isothermal exposure for 0.5-1 hours, after which, without changing the temperature in the furnace, turned on the hydraulic press. The pressure on the powder briquette was transmitted in the vertical direction through the mold punch, on which the movable stop in the furnace lid pressed against the traverse steel plate. After turning on the press, the pressure on the powder briquette was slowly increased to a value of 1.5-2 tf / cm ² . Then did isobaric-isothermal exposure for 20-45 minutes. After that, the pressure of the hydraulic press was gradually reduced and the furnace was inertially cooled to ambient temperature. After the pressed ceramic obtained was not transparent enough. In addition, significant stresses were present in it, since annealing of the obtained ceramics in the mold was difficult.

Heat treatment of ceramics in an active fluorinating atmosphere.

To achieve the highest optical characteristics, the obtained ceramic billet was subjected to heat treatment in an atmosphere of gaseous carbon tetrafluoride, and to relieve residual heat-elastic stresses, heat treatment was combined with annealing, which was carried out at given heating and cooling rates of the material. The material was annealed in a fluorinating medium as follows. The pressed ceramic sample was placed in a special graphite form with which the sample had only point contact. Thus, almost the entire surface of the sample was open for active interaction with a fluorinating gaseous agent. A vacuum system was first created in the furnace chamber by a system of vacuum pumps to remove air from the furnace chamber. Then the furnace was filled with a fluorinating agent - gaseous carbon tetrafluoride. Next, the furnace was heated to a temperature of 1000-1300 ° C at a rate of 30-50 ° C / h and isothermal exposure was made for 20-60 hours. During the exposure, the pressure of carbon tetrafluoride was maintained in the range of 800-1100 mm Hg. After exposure, the furnace was cooled at a rate of 25-50 ° C / h to ambient temperature.

As a result, we obtained optical ceramics based on fluorides of alkaline-earth and rare-earth elements, transparent in the wavelength range from 0.2 to 10 μm and exhibiting laser or scintillation properties.

The compositions of optical ceramics obtained by the proposed method, and the affiliation of ceramics of each composition to the laser or scintillation type of material are shown in the table.

Table Composition and type of ceramic material The composition of the ceramic material Rare earth fluoride concentration Type of ceramic material CaF ₂ : YbF ₃ 1-5 mol.% laser material CaF ₂ : ErF ₃ 1-10 mol.% laser material CaF ₂ : NdF ₃ 0.5-1 mol% laser material CaF ₂ : TmF ₃ 1-6 mol.% laser material BaF ₂ : CeF ₃ 0.01-0.12 mol.% scintillation material BaF ₂ : ScF ₃ 0.3-1 mol% scintillation material BaF ₂ : TmF ₃ 0.25-3 mol% scintillation material

The invention is illustrated by the following drawings.

Figure 1 shows the transmission spectrum of a ceramic sample of composition CaF ₂ : 3 mol.% YbF ₃ with a sample thickness of 5 mm The spectrum represents the dependence of the radiation transmittance of the material (τ,%) on the wavelength of this radiation (λ, μm) in the wavelength range from 0.2 to 8 μm.

Figure 2 shows the transmission spectrum of a ceramic sample with a CaF ₂ composition: 10 mol% ErF ₃ with a sample thickness of 6 mm. The spectrum represents the dependence of the radiation transmittance of the material (τ,%) on the wavelength of this radiation (λ, μm) in the wavelength range from 0.2 to 8 μm.

Figure 3 presents the absorption spectrum of a ceramic sample with a composition of CaF ₂ : 0.5 mol.% NdF ₃ . The spectrum represents the dependence of the radiation absorption coefficient of the material (K, cm ^-1 ) on the wavelength of this radiation (L, μm) in the wavelength range from 0.25 to 3.25 μm.

Figure 4 presents the luminescence spectrum of a ceramic sample with a composition of CaF ₂ : 0.5 mol.% NdF ₃ . The spectrum represents the dependence of the luminescence intensity of the material (I, rel. Units) on the wavelength (L, μm) in the wavelength range from 0.8 to 1.5 μm.

Figure 5 presents the decay curve of the luminescence of neodymium ions in ceramics composition CaF ₂ : 0.5 mol.% NdF ₃ . The curve represents the dependence of the luminescence intensity of the material (I, rel. Units) on time (t, ms).

Figure 6 presents the transmission spectrum of a ceramic sample with a composition of BaF ₂ : 0.12 mol.% CeF ₃ . The spectrum represents the dependence of the radiation transmittance of the material (τ,%) on the wavelength of this radiation (λ, μm) in the wavelength range from 0.2 to 12 μm.

Figure 7 presents the x-ray luminescence spectrum of a ceramic sample with a composition of BaF ₂ : 0.12 mol.% CeF ₃ . The spectrum represents the dependence of the luminescence intensity of the material (I, rel. Units) on the wavelength (L, μm) in the wavelength range from 0.2 to 0.6 μm.

On Fig presents the x-ray luminescence spectrum of a ceramic sample of composition BaF ₂ : 0.5 mol.% ScF ₃ . The spectrum represents the dependence of the luminescence intensity of the material (I, rel. Units) on the wavelength (L, μm) in the wavelength range from 0.2 to 0.5 μm.

Example No. 1. The synthesis of CaF ₂ : 3 mol% YbF ₃ raw powder was carried out using calcium carbonates, ytterbium and a 45% solution of hydrofluoric acid. The resulting reaction product of carbon dioxide salts with acid was dried at 100 ° C and then calcined at 700 ° C. The result was a powder of CaF ₂ composition: 3 mol% YbF ₃ , which was heat-treated in vacuum (10 ^-5 mm Hg) at a furnace temperature of 1320 ° C for 2 hours. After heat treatment, the briquette of the powder was pressed in vacuum (10 ^-4 mm Hg) at a temperature of 1150 ° C, with an applied pressure of 2 tf / cm ² on the sample for 30 minutes. After the hot pressing step, the sample was sent for heat treatment in CF ₄ gas at a temperature of 1200 ° C for 30 hours.

The ceramic sample synthesized in this way was transparent in the region of 0.2–8 μm. The transmission spectrum of this sample with a thickness of 5 mm is shown in FIG. The spectrum contains an absorption band inherent in Yb ^{2+ ions} (0.3-0.4 μm) and an absorption band inherent in Yb ³⁺ ions (0.9-1 μm). This sample was used to generate laser radiation in the wavelength range of 1.025-1.040 μm, when excited by radiation with a wavelength of 0.967 μm. The generation efficiency was 45%.

Example No. 2. The synthesis of the raw powder CaF ₂ : 10 mol.% ErF _{3 was} carried out using calcium carbonates, erbium and a 45% solution of hydrofluoric acid. The resulting reaction product of carbon dioxide salts with acid was dried at 100 ° C and then calcined at 700 ° C. The result was a powder of the composition CaF ₂ : 10 mol% ErF ₃ , from which a ceramic sample was obtained analogously to example 1.

The synthesized ceramic sample was transparent in the region of 0.2–8 μm.

The transmission spectrum of this sample with a thickness of 6 mm is presented in figure 2.

Example No. 3. By the interaction of neodymium and calcium carbonates with a solution of 50% hydrofluoric acid, a mixture of calcium fluorides and neodymium was obtained, which was dried at 90 ° C and calcined at 800 ° C. The resulting powder of the composition CaF ₂ : 0.5 mol% NdF _{3 was} placed in a mold in a vacuum oven and processed at a pressure in the system of 10 ^-5 mm Hg. and a temperature of 1150 ° C for 2 hours. The resulting porous powder briquette was subjected to uniaxial pressing in vacuum (10 ^-4 mm Hg) at a temperature of 1100 ° C, applying a pressure of 2 tf / cm ² to the sample for 20 minutes. After the hot pressing process, the obtained optical ceramic was heat treated in a CF ₄ gas atmosphere at a temperature of 1200 ° C. for 20 hours. Figure 3 and 4 show the spectra of the absorption coefficient and luminescence of the obtained ceramic sample, respectively, and Figure 5 is the decay curve of the luminescence of neodymium ions in this ceramic.

Example 4. The synthesis of raw powder BaF ₂ : 0.12 mol.% CeF _{3 was} carried out using barium carbonates, cerium and 45% solution of hydrofluoric acid. The resulting reaction product of carbonic salts with acid was dried at 100 ° C and then calcined at 800 ° C. The result was a powder of composition BaF ₂ : 0.12 CeF ₃ , which was placed in a mold in a vacuum oven and treated at a pressure in the system of 10 ^-5 mm Hg. and a temperature of 1200 ° C for 1 hour. The obtained porous powder briquette was installed in the mold and subjected to uniaxial pressing in vacuum (10 ^-4 mm Hg) at a temperature of 1000 ° C, applying a pressure of 1.5 tf / cm ² to the sample for 15 min. After the hot pressing process, the obtained optical ceramic was heat treated in a CF ₄ gas atmosphere at a temperature of 1200 ° C. for 20 hours.

As a result, a ceramic material was obtained that was transparent in the spectral range from 0.2 to 12 μm. The transmission spectrum of this sample is presented in Fig.6. A 5 × 10 × 15 mm sample was made from this ceramic to measure scintillation characteristics. An X-ray luminescence spectrum was recorded in the range from 200 to 600 nm (Fig. 7) under continuous irradiation of the sample with X-ray radiation. In the curve of the X-ray luminescence spectrum, there were low-intensity bands located at 220 and 270 nm, and an intense band in the region of 310-320 nm. The luminescence kinetics was measured on this sample, which showed that the luminescence time corresponding to the luminescence band at 220 nm is 2 ns, for the band located at 270 nm, 60 ns, and for the luminescence band in the region of 310-320 nm, 400 ns.

Example 5. The synthesis of raw powder BaF ₂ : 0.5 mol.% ScF _{3 was} carried out using barium carbonates, scandium and a solution of hydrofluoric acid. The resulting reaction product of carbonic salts with acid was dried at 100 ° C and then calcined at 800 ° C. From the synthesized powder, a ceramic of composition BaF _{2 was} obtained: 0.5 mol% ScF ₃ analogously to example No. 4. The resulting ceramics were transparent in the region of 0.2–10 μm and possessed scintillator properties. The X-ray luminescence spectrum of a ceramic sample made in the form of a parallelepiped polished on all sides with dimensions 5 × 5 × 15 mm is shown in Fig. 8.

Claims (3)

1. A method of producing optical ceramics, including heat treatment of an initial mixture of alkaline earth and rare earth metal fluorides, its briquetting, uniaxial hot pressing of a briquette to obtain a polycrystalline ceramic sample, and its heat treatment in an active fluorinating gas medium, characterized in that the raw materials are synthesized initially using powder alkaline earth and rare earth metal fluorides obtained by the interaction of a mixture of carbon dioxide salts of alkaline earth and rare earth nogo metals and hydrofluoric acid solution, thereby producing the synthesized powder of alkaline earth fluorides and rare earth elements, which is briquetted by treatment under vacuum at a temperature of 1000-1350 ° C and a pressure of 10 ^-4 -10 ^-5 Torr within 1-3 hours. 2. The method according to claim 1, characterized in that a mixture of fluorides of alkaline earth and rare earth elements of the following composition is used: MeF ₂ -X% TRF ₃ , where Me = Ba, Ca, a TR = Nd, Yb, Er, Ce, Sc, Tm, X is the concentration of the dopant, varying from 0.01 to 10 mol%. 3. The method according to claim 1 or 2, characterized in that the initial mixture in the form of barium fluoride, calcium and rare earth elements is obtained using carbonates of selected specific starting components and a concentrated solution of hydrofluoric acid, preferably 45-50%.

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